This application claims the priority benefit of Taiwan application serial no. 88121080, filed Dec. 2, 1999.
1. Field of the Invention
The present invention relates to a variable focus lens system. More particularly, the present invention relates to a high-resolution variable lens system having an extra-long back focal length with telecentric design.
2. Description of the Related Art
Because of an increase in the resolution of the liquid crystal display panel inside a liquid crystal projector, image resolution of the projection lens system must increase correspondingly. An earlier version of liquid crystal display panel was a transparent type, and hence overall image resolution was lower. When the liquid crystal panel is implemented in a projector, the projection lens associating with the display panel usually does not need a long back working distance, because it typically uses a dichromic prism to perform color synthesis.
In recent years, however, a reflective liquid crystal display panel having more than one million thirty thousand pixels, with each pixel size smaller than 20 micrometers, has been developed. To use the reflective liquid crystal panel in a projector, sufficient space must be reserved between the liquid crystal panel and the projection lens system for positioning a polarizing beam splitter prism and a dichromic cross prism. In other words, the projection lens must have a sufficiently long back working distance for housing the two optical components. In addition, when incident light is perpendicular to the liquid crystal panel, a relatively good contrast is obtained on the liquid crystal panel. Further, the dichromic prism also does not need a gradient coating to form the dichromic coating film thereon, and the fabrication is reduced. In this consideration, an illuminating system of the projector generally takes a telecentric design. This means that the exit pupil of the illuminating system is positioned at a rather infinite distance.
In order to achieve the highest efficiency of light output, the projection lens must be a telecentric design associating with the illuminating system. An another advantage of the telecentric protection lens is that an uneven magnification power caused by location errors while adjusting position of the liquid crystal display panel can be reduced. Particularly, as the pixel size of the display panel is greatly small, the telecentric projection lens allows the adjustment of the display panel to be much easier. This also can further reduce the fabrication cost.
Conventional protection lens assemblies, such as the inventions described in Japanese patents No. JP8036132 and No. JP8201690, have a sufficiently long back focal length. However, they are not a telecentric design. Although the invention described in the Japanese patent No. JP8297243 has a sufficiently long back focal length as well as a telecentric design, the projecting angle is too small.
Accordingly, one object of the present invention is to provide a high-resolution variable focus lens system having an extra-long back focal length with telecentric design. The lens system can be used in a liquid crystal projector that requires a long back focal length and has a large number of pixels. Not only is the lens system capable of producing a high-quality, high-resolution image, but the angle of projection of the lens system is large sufficiently for producing a large image within a relatively short projection length.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an optical component. The optical component includes a high-resolution variable focus lens system having an extra-long back focal length with telecentric design. From the screen to the image (liquid crystal panel), the high-resolution variable focus lens system includes three groups of lenses in sequence. A first group of lenses is used for focusing and zooming. The first group of lenses having negative power includes three lenses counting from one to three. A second group of lenses is used for zooming. The second group of lenses having negative power includes two lenses counting from four to five. A third group of lenses is also used for zooming. The third group of lenses having positive power includes six lenses counting from six to eleven.
Focal length of the lens system can be changed by varying the distance between the first group and the second group of lenses as well as the second group and the third group of lenses along the optical axis. The variable focus lens system must satisfy the following conditions:
2.15fWxe2x89xa6|f1|xe2x89xa62.89fW;xe2x80x83xe2x80x83(1)
xe2x80x834.86fWxe2x89xa6|f2|xe2x89xa69.82fW;xe2x80x83xe2x80x83(2)
1.65fWxe2x89xa6f3xe2x89xa61.74fW;xe2x80x83xe2x80x83(3)
0.37f3xe2x89xa6t12xe2x89xa60.42f3;xe2x80x83xe2x80x83(4)
and
N6xe2x89xa71.66,xe2x80x83xe2x80x83(5)
where f1 to f3 are the focal lengths of the first, the second and the third group of lenses, respectively; fW is the focal length of the variable focus lens system at wide angle; and t12 is the distance on the optical axis between the sixth lens and the seventh lens while N6 is the refractive index of the sixth lens.
According to the embodiment of this invention, a high-resolution variable focus lens system with a long back focal length, a telecentric design, and a wider projection angle is achieved. The lens system is capable of producing a high-quality image at various projection distances. When the lens system is used inside a liquid crystal projector that requires a long working distance and a high resolution, sufficient space is reserved for implementing a polarizing beam splitter prism and a dichromic cross prism. Furthermore, the liquid crystal display panel can be easily aligned. In addition, if a large image needs to be projected, only a relatively short projection distance is demanded.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.